Suggest borrowing when trying to coerce unsized type into dyn Trait

3 files changed, 28 insertions, 0 deletions

diff --git a/src/test/ui/issues/issue-14366.stderr b/src/test/ui/issues/issue-14366.stderr
index d5dab561dde..b96b07c91a1 100644
--- a/src/test/ui/issues/issue-14366.stderr
+++ b/src/test/ui/issues/issue-14366.stderr
@@ -6,6 +6,10 @@ LL |     let _x = "test" as &dyn (::std::any::Any);
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: required for the cast to the object type `dyn Any`
+help: consider borrowing the value, since `&str` can be coerced into `dyn Any`
+   |
+LL |     let _x = &"test" as &dyn (::std::any::Any);
+   |              +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/mismatched_types/cast-rfc0401.stderr b/src/test/ui/mismatched_types/cast-rfc0401.stderr
index 5f11e4ded80..84220ea172a 100644
--- a/src/test/ui/mismatched_types/cast-rfc0401.stderr
+++ b/src/test/ui/mismatched_types/cast-rfc0401.stderr
@@ -224,6 +224,10 @@ LL |     let _ = fat_v as *const dyn Foo;
    |
    = help: the trait `Sized` is not implemented for `[u8]`
    = note: required for the cast to the object type `dyn Foo`
+help: consider borrowing the value, since `&[u8]` can be coerced into `dyn Foo`
+   |
+LL |     let _ = &fat_v as *const dyn Foo;
+   |             +
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/cast-rfc0401.rs:62:13
@@ -233,6 +237,10 @@ LL |     let _ = a as *const dyn Foo;
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: required for the cast to the object type `dyn Foo`
+help: consider borrowing the value, since `&str` can be coerced into `dyn Foo`
+   |
+LL |     let _ = &a as *const dyn Foo;
+   |             +
 
 error[E0606]: casting `&{float}` as `f32` is invalid
   --> $DIR/cast-rfc0401.rs:71:30
diff --git a/src/test/ui/unsized/unsized-fn-param.stderr b/src/test/ui/unsized/unsized-fn-param.stderr
index b498259efe7..3eecca0fa09 100644
--- a/src/test/ui/unsized/unsized-fn-param.stderr
+++ b/src/test/ui/unsized/unsized-fn-param.stderr
@@ -6,6 +6,10 @@ LL |     foo11("bar", &"baz");
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: required for the cast to the object type `dyn AsRef<Path>`
+help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<Path>`
+   |
+LL |     foo11(&"bar", &"baz");
+   |           +
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/unsized-fn-param.rs:13:19
@@ -15,6 +19,10 @@ LL |     foo12(&"bar", "baz");
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: required for the cast to the object type `dyn AsRef<Path>`
+help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<Path>`
+   |
+LL |     foo12(&"bar", &"baz");
+   |                   +
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/unsized-fn-param.rs:16:11
@@ -24,6 +32,10 @@ LL |     foo21("bar", &"baz");
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: required for the cast to the object type `dyn AsRef<str>`
+help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<str>`
+   |
+LL |     foo21(&"bar", &"baz");
+   |           +
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/unsized-fn-param.rs:18:19
@@ -33,6 +45,10 @@ LL |     foo22(&"bar", "baz");
    |
    = help: the trait `Sized` is not implemented for `str`
    = note: required for the cast to the object type `dyn AsRef<str>`
+help: consider borrowing the value, since `&str` can be coerced into `dyn AsRef<str>`
+   |
+LL |     foo22(&"bar", &"baz");
+   |                   +
 
 error: aborting due to 4 previous errors